When building a vehicle, selecting a TREMEC 5- or 6-speed transmission gives you the opportunity to change the vehicle’s axle gear ratio in order to maximize the driving experience. The TREMEC Gear Ratio Calculator makes it easy to experiment with the affect that various ratios will have on the engine rpm at various speeds, letting you choose the ratio that will be best for the way you want to use your vehicle.
On the street, having a great match with the transmission gearing and the rear axle gear results in good drivability in stop and go traffic as well as a desirable highway cruise rpm. You can also avoid “lugging down” the engine while cruising at normal street and highway speeds by checking that the engine rpm will be within desired ranges.
At the track, having the right axle gear for your transmission gears can often make the difference between winning and losing. While important with all types of racing, the ability to see specific engine rpm at various vehicle speeds is critical for setting up a car correctly for auto cross and road racing.
The TREMEC gear ratio calculator provides an easy way to calculate and see how your chosen TREMEC transmission will act with any rear axle gear, or any other transmission for that matter. It’s ideal for comparing your vehicle with the existing transmission and what will happen when you change to an off-the-self or customized TREMEC transmission. Besides the already preloaded manual transmission profiles to choose from, you enter the gear ratio data for 3-, 4-, 5-, or 6-speed transmissions manually and see the speed you would be at in each gear to the rpm inputted into the calculator. Besides cruising speeds, for racing you can calculate the vehicle speed you’d be at for the optimal shift points of your engine.
Here are some examples of how the calculator works in relation to those different scenarios.
Using a typical muscle car combo with a Muncie close-ratio 4-speed, here is the mile-per-hour you reach in each gear at 2,600 rpm. In fourth gear you’re only going 58 mph, still under a normal highway cruising speed of 65-70. To drive at those speeds, you’ll be turning the engine even higher, creating more stress on the engine and consuming a lot of fuel. Replacing the old Muncie with a modern TREMEC TKO 5-speed that has a .82 overdrive and a more optimal first and second gear, you end up with a cruising rpm right around 2,000, but still have great stoplight-to-stoplight and dragstrip performance. This gives you the best of both worlds.When going to a dual overdrive manual transmission like the TREMEC Magnum 6-speed with 2.97 first gear and .50 overdrive, it opens the door for more rear axle gearing to increase street performance, and still have highway cruising capability. But not enough rear gear and you end up cruising at too low of an rpm which can cause the engine to lug. In this snapshot, we have a typical combo of 3.23 gear, 28-inch tall tire, and a cruising rpm of 2,200. In fifth gear at 2,200 rpm you’re already going 76 mph. Changing the rear gear ratio to 3.73:1 or 4.10:1 would be much better.Using the calculator, we inputted a much lower rear gear, one that matches up better with the higher rpm capabilities of modern engines like GM LS and LT V8s, the Ford Modular and Coyote V8s, and Gen III/IV Hemi engines. Now at normal highway speeds, cruising at 2,200 rpm fifth gear is much better suited for 55 and 65 mph cruising, and sixth gear is ready for interstate cruising of 70 mph and above. At the same time, first through fourth gears will give great acceleration on the street and at the track with high-rpm shifting. For racers, the TREMEC gear ratio calculator is valuable for figuring out shift points and correlating mph to aid in tuning. In this shot, we have the combo of a 2003 Ford Mustang Cobra raced in NMRA competition. The car uses a Magnum 6-speed with 2.66 first gear. Shifting at 6,300 rpm (optimal for this combo) you know what the corresponding mph will be.
